Connecting a three-phase asynchronous electric motor to a single-phase network. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Connecting a three-phase asynchronous electric motor to a single-phase network. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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The necessary equipment in the home laboratory of a radio amateur is a drilling and grinding machine. However, not everyone can buy them, and they are expensive. Buying an asynchronous three-phase electric motor in order to make the necessary machine on its basis is much easier and, most importantly, cheaper. The main problem is connecting such a motor to a single-phase network.

Typically, the ends of the windings of an asynchronous three-phase electric motor are brought out to a three- or six-terminal block. If the block is three-terminal, then the phase stator windings are connected by a star or a triangle. If it is six-terminal, the phase windings are not connected to each other.

In the latter case, it is important to connect them correctly. When turned on by a star, the winding terminals of the same name (beginning or end) should be combined into a zero point. In order to connect the windings in a triangle, it is necessary to connect the end of the first winding to the beginning of the second, the end of the second to the beginning of the third, and the end of the third to the beginning of the first.

But what if the terminals of the motor windings are unmarked? Then proceed as follows. Three windings are determined with an ohmmeter, conventionally designating them I, II and III. To find the beginning and end of each. any two are connected in series and an alternating voltage of 6 ... 36 V is applied to them. An alternating current voltmeter is connected to the third winding (Fig. 1). The presence of alternating voltage indicates that. that the windings I and II are connected in accordance, and the absence of voltage is opposite. In the latter case, the conclusions of one of the windings should be reversed. After that, the beginning and end of the windings I and II are marked (the conclusions of the windings I and II of the same name in Fig. 1 are marked with dots). To determine the beginning and end of the winding III, the windings are interchanged, for example, II and III, and the measurements are repeated according to the method described above.

Connecting a three-phase asynchronous electric motor to a single-phase network

A three-phase asynchronous electric motor can be operated from a single-phase network with a phase-shifting capacitor. Its capacitance (in μF) can be estimated by the formula: C = k I / Ucoil where k is a coefficient depending on the connection of the windings: If is the rated phase current of the electric motor. A: Ucoil - voltage of a single-phase network. B. If the motor windings are connected by a star (Fig. 2). k = 2800, and if a triangle (Fig. 3) - k = 4800.

Connecting a three-phase asynchronous electric motor to a single-phase network

Here you can use paper capacitors MBGCH. K42-19 for a rated voltage not less than the mains voltage. It should be remembered that even with a properly selected capacitor capacity, the electric motor develops power no more than 50 ... 60% of the nominal.

Author: N. Shatalov, Irba village, Krasnoyarsk Territory

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